Key routes in Baghdad were locked down on Wednesday as Al-Qaeda's front group in Iraq claimed responsibility for a wave of deadly blasts targeting security for a landmark Arab summit next week.
The tightened measures came a day after nationwide gun and bomb attacks killed 50 people and wounded 255 on the ninth anniversary of the start of the US-led invasion of Iraq.
The country was struck with more unrest on Wednesday, with five people, including three young children, killed.
In a statement posted on jihadist forum Honein, the Islamic State of Iraq declared it was behind the attacks against several "official posts, and security and military posts" in the country.
"The lions (jihadists) of Al-Sunna... of the Islamic State of Iraq simultaneously attacked the authorities' security plans... for the meeting of Arab tyrants in Baghdad," said the statement dated March 20.
These attacks "destroyed the plans of the head of Iraqi security chiefs in the space of a few hours," it added.
Tuesday's violence rocked 20 towns and cities spanning the northern oil hub of Kirkuk and the Shiite shrine city of Karbala, south of Baghdad, from 7:00 am (0400 GMT), and continued through the day.
The spate of attacks bore the hallmarks of Al-Qaeda, which typically tries to launch coordinated nationwide mass-casualty bombing campaigns.
They struck despite unprecedented levels of security in Baghdad as part of preparations for the March 27-29 summit of the Arab League, the first of the 22-member bloc to be held in the Iraqi capital in more than 20 years.
Wednesday's yet tougher measures worsened already choking traffic in Baghdad.
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AFP journalists reported full or partial closures of key routes, while roads that remained open saw increased numbers of checkpoints and security forces, and virtually all of the bridges that traverse the Tigris River were also shut.
Despite the ramped up security, gunmen broke into a house in south Baghdad and slaughtered a 25-year-old mother and her three young children, security and medical officials said. Another woman was gunned down in central Iraq, according to police.
Tuesday's attacks drew swift condemnation from around the world, with United Nations envoy Martin Kobler describing them as "atrocious".
White House spokesman Jay Carney said the United States "strongly condemns" the violence, while Britain's Middle East minister Alistair Burt described it as "cowardly."
Iraqi parliament speaker Osama al-Nujaifi condemned the "brutal criminal" attacks, and said they were part of efforts by Al-Qaeda to "derail the Arab summit.
Following the attacks, the government declared a week of public holidays from March 25 to April 1.
Coupled with Kurdish New Year festival Nowruz on Wednesday and the weekly Muslim day of prayer on Friday, much of Iraq will be largely closed until after the summit.
Security forces have mooted the possibility of imposing a city-wide curfew on March 29, when Arab leaders are expected in Baghdad for the first such meeting in the Iraqi capital since Saddam Hussein's 1990 invasion of Kuwait.
Officials insist Iraq's forces are capable of maintaining security for the summit, and have drafted in an additional 4,000-odd policemen and soldiers, but admit they may need to effectively shut down Baghdad to do so.
Tuesday's violence was Iraq's deadliest day since January 14, when 53 people were killed in a suicide bombing outside the southern port of Basra.